The present invention relates to a high-frequency signal transmitting device which is used in a high-frequency band such as a microwave band and an extremely high frequency band and is able to accommodate a semiconductor device and particularly to a high-frequency signal transmitting device having a good transmission characteristic in a high-frequency band.
A high-frequency signal transmitting device or layered structure for high-frequency signal transmission having a construction shown in FIGS. 76A and 76B is known. FIG. 76A is a plan view of the high-frequency signal transmitting device, and FIG. 76B is a vertical sectional view taken along the line 76B—76B of FIG. 76A. The high-frequency signal transmitting device shown in FIGS. 76A and 76B is formed by using a layered substrate 510 in which a plurality of dielectric layers (dielectric substrates) 500 rectangular in plan view are placed one over another along vertical direction of FIGS. 76A and 76B. On the upper surface of the uppermost dielectric layer 500 of this layered substrate 510 and on the lower surface of the bottommost dielectric layer 500, signal wiring conductors 520, 530 are provided at such positions facing each other. A grounding conductor 550 having such a shape as to surround a circular grounding-conductor non-forming area 540 defined in the center of each dielectric layer 500 is provided on each of the upper surfaces of the intermediate dielectric layers 500 located between the uppermost and bottommost dielectric layer 500 and the upper surface of the bottommost dielectric layer 500.
Signal via conductors 560 are so provided at positions of the respective dielectric layers 500 corresponding to the centers of the grounding-conductor non-forming areas 540 as to vertically penetrate the dielectric layers 500. The signal via conductor 560 of the uppermost dielectric layer 500 is connected with the signal wiring conductor 520 via a signal-wiring connecting conductor 570 provided on the upper surface of the uppermost dielectric layer 500, and the signal via conductor 560 of the bottommost dielectric layer 500 is connected with the signal wiring conductor 530 via a signal-wiring connecting conductor 580 provided on the lower surface of the bottommost dielectric layer 500.
By providing the grounding conductors 550 on the upper surfaces of the intermediate dielectric layers 500 and the bottommost dielectric layer 500 and providing the respective dielectric layers 500 with the signal via conductors 560 in this way, the layered substrate 510 is allowed to have a coaxial line construction, thereby forming a high-frequency signal transmitting device.
However, when a sample as described below was prepared and a high-frequency characteristic thereof was studied, it was found out that the high-frequency signal transmitting device having the conventional construction did not have a good high-frequency transmission characteristic.
Specifically, the high-frequency signal transmitting device having the construction of FIGS. 76A and 76B was constructed as follows. The layered substrate 510 was formed by placing nine dielectric layers 500 having a relative dielectric constant of 9.2 and a thickness of 0.2 mm one over another, the signal wiring conductors 520, 530 and the signal-wiring connecting conductors 570, 580 of the uppermost and bottommost dielectric layers 500 were formed to have a width of 0.16 mm, whereas the signal via conductors 560 of the respective dielectric layers 500 were formed to have a circular cross section of a diameter of 0.1 mm, and the grounding conductors 550 of the intermediate and bottommost dielectric layers 500 were formed such that the grounding-conductor non-forming areas 540 had a circular shape of a diameter of 0.84 mm. Further, a distance between an end of the signal wiring conductor 520 at a side opposite from the signal-wiring connecting conductor 570 and an end of the signal wiring conductor 530 at a side opposite from the signal-wiring connecting conductor 580 was set to be 2.0 mm in plan view.
The high-frequency characteristic between the ends of the signal wiring conductors 520 and 530 was obtained for the sample thus constructed by an electromagnetic field simulation, a characteristic curve having a frequency characteristic as shown in a graph of FIG. 77 was obtained. FIG. 77 shows a frequency characteristic of a reflection coefficient (unit: dB) which is a rate of reflected and returned signals to incident high-frequency signals, wherein horizontal axis represents frequency (unit: GHz) and vertical axis represent reflection frequency (unit: dB) as an evaluation index of a reflected quantity of the signal. As is clear from FIG. 77, the conventional high-frequency signal transmitting device having the construction of FIGS. 76A and 76B can be understood not to have a good high-frequency transmission characteristic.